1. Field of the Invention
The present invention relates to communication systems, and in particular to encrypting of information for transmission in a communication system.
2. Background Information
Secure transmission of information is of concern when transferring content over a public network such as the Internet. In some cases, an additional concern is to ensure that the recipient, or anyone who intercepts the information, is not able to forward the information to others. For example, a vendor of content such as digitized music may sell the content in a form readily playable on any personal computer. A recipient of the content could deprive the vendor of revenue by forwarding the content to others, or by posting the content in a file on a server for unlimited access by others.
The vendor can, of course, encrypt the content to protect against the content being intercepted by an unintended recipient. Many encryption systems and protocols exist to secure electronic transmission between a vendor and a customer. For example, Pretty Good Privacy (PGP) is a public domain encryption system that uses public/private key protocols such as Diffie-Hellman, as disclosed in U.S. Pat. No. 4,200,770, and Rivest-Shamir-Adleman (RSA), as disclosed in U.S. Pat. No. 4,405,829, the disclosures of which are hereby incorporated by reference in their entirety.
In addition to encrypting information for secure transmission, public/private key systems have been developed to protect against an authorized recipient (e.g., a customer) redistributing the information to others. For example, known systems distribute content in a form that is not freely readable, but rather is encrypted to be playable only on a particular device of a customer who has purchased the content. In this case, the content can be purchased and transported over a network, but the delivered file which contains the content will be playable only on the specified customer's device. If the customer forwards the file to others, or if the file is improperly intercepted, the content is unplayable in other devices.
An exemplary known method used to implement public/private key encryption of content, to protect against a customer distributing unauthorized copies, is shown in FIG. 1. After receiving a customer's public key, the vendor encrypts the content (e.g., digitized music) using the customer's public key in step 100 (for example, the public key of the customer's playback device). The encrypted content can be transmitted to the customer's playback device, for instance via the Internet, in step 102. The encrypted content can be transmitted to the playback device directly or stored on the customer's computer. In step 104, the playback device decrypts the content using an embedded private key (e.g., plays the digitized music), in a secure manner, such that the unencrypted content is not directly available to the customer to modify or forward as a user file. The encrypted data, even if stored on the customer's computer or a public network, cannot be used by the customer or others without the secure playback device which includes the private key.
Prior art systems require that the entire data file that comprises the content be encrypted every time a copy is purchased by a customer, as the public keys of each customer/device will be different. Additionally, on the customer's system, the entire data file is decrypted each time the content is accessed. When the number of uses by a given customer is to be limited, the computational burden is even greater because additional use limitation protocols are included in the encryption protocols.
For content that involves large data files, such as video on demand, 3D animations, high resolution images, high fidelity music, and the like, known systems place a large computational burden on the vendor's server. Additionally, known systems cannot take advantage of methods to alleviate network congestion, such as caching, the use of intermediate proxies, and the like, because each user downloads the file directly from the vendor's server.